The present invention relates to a method for detecting methylisothiocyanate and to a device for performing the method.
It is often necessary for soil used in agriculture to be fumigated before the next sowing or replanting, for instance by treatment with a fungicide or nematicide. For instance, methylisothiocyanate (MITC) is used to prepare soils both in greenhouses and on open land for the cultivation of vegetables.
When Dazomet is used, methylisothiocyanate is released slowly through the moisture of the soil. MITC is the actual biologically effective agent in this case. The use of metam-sodium (sodium-M-methyldithiocarbamate) as a soil fumigant is also known. Metam-sodium likewise releases MITC as the actual active ingredient.
MITC is a solid at room temperature (melting point 32 to 38° C.) and evaporates slowly and in the process destroys animal pests, fungi, and plants in the soil, so that useful plants, especially vegetables, can germinate and grow without competition. MITC is toxic both to humans and to the useful plants. It is therefore important to protect humans; moreover, the soil must be free of MITC before sowing.
After each use of a soil decontaminant, a certain waiting period must be observed until resowing or replanting of useful and cultivated plants, in order to assure that the soil decontaminant has decomposed extensively enough that there is no need to fear adverse effects on the resowing or replanting. For the farmer, it is of decisive importance to obtain a reliable statement about the length of the waiting period.
The detection of isothiocyanates with inorganic reagents is known per se. For instance, former East German Patent Disclosure DD 285 196 describes a test paper for detecting isocyanates and isothiocyanates, which comprises a paper that is saturated with pyridinium salts. For detecting the aforementioned substances, the test paper is put into contact with the substance to be tested, and then, by vapor deposition of ammonia, an intensive yellowish-orange to orange-red/brown coloration develops.
The known detection methods, however, have proved to be insensitive and/or too expensive in practice.